Method and apparatus for crystal analysis

ABSTRACT

The method of measuring crystallographic orientations, crystal systems or the like of the surface of a specimen has steps of: irradiating the specimen with an ion beam; measuring tho secondary electrons generated by the irradiation of the ion beam; repeating the irradiation of the ion beam and the measurement of the secondary electrons with each variation in an angle of incidence of the ion beam with respect to the specimen; and determining the crystalline state based on the variation in the amount of the secondary electrons corresponding to the variation of the angle of incidence.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of crystal analysis and anapparatus for crystal analysis capable of analyzing crystalline statessuch as the crystallographic orientations of individual crystal grainson the surface of a specimen.

2. Description of the Related Arts

The recent development of micromachining technologies has come torequire the technologies for analyzing crystal system andcrystallographic orientations of crystal grains on a solid surface orthe like. For example, a fine copper (Cu) wiring formed by a platingprocess has been employed for a coil wiring of a write element for amagnetic head employed in a hard-disk drive. In this copper wiring, theorientations of microcrystals and the structures of crystal-grainboundaries make a difference in a resistance value of the wire, causingvariations in the characteristics of the magnetic head. For this reason,control of crystal growth has become one of the requirements forfabricating a magnetic head of high reliability and thus grasping ofdiameters of microcrystal grains, states of grain boundaries andcrystallographic orientations has become of great interest.

Concerning the diameters of crystal grains and states of grainboundaries, it is easy to obtain knowledge through observations by anelectron microscope and observations by a scanning ion microscope (SIM).As a practical method available for obtaining the knowledge specificallyon the crystallographic orientations of the copper crystal grains thatmake up the copper wiring described above, however, there has been knownonly the EBSP (Electron BackScattering Pattern method or the ElectronBackScattering diffraction Pattern) method. In the EBSP method, anelectron beam impinges on a specimen at a large incidence angle in ascanning electron microscope (SEM); the electron beam experiencesreflections and diffraction in the specimen; and is scattered backwardsto form a diffraction image. This diffraction image (i.e., diffractionpattern) varies in its bandwidth and intensity depending on thecrystalline structure at the incident position of the electron beam.Accordingly, the crystal system and the crystallographic orientation canbe determined by analyzing the obtained diffraction pattern. Performingthe analysis of the pattern while scanning a specimen surface with theelectron beam enables obtaining the knowledge on the two-dimensionaldistribution of the crystallographic orientations on the specimensurface.

However, a problem has been that, because, in the EBSP method, theelectron beam impinges on a specimen surface at a large angle ofincidence, minute unevennesses of the surface affect on the result ofthe analysis and the correspondence between the distribution of thecrystallographic orientations observed through the EBSP method and themicroscopic image observed through the ordinary scanning microscopicphotographs cannot easily be identified. Furthermore, because thediffraction pattern is caused by the Bragg reflection from crystalgrains, it is basically difficult to have the resolution (ie., spatialresolving power) raised higher than the existing value, practically theresolution being of the order of several tens of nanometers.

An incidence angle described herein stands for the angle measured fromthe direction of the normal of the plane of incidence.

While a crystal system and a crystallographic orientation can be decidedby the X-ray diffraction method as well, it is difficult in the case ofthe X-ray to narrow the beam and consequently the resolution is of theorder of ten micrometers. Furthermore, the penetration depth of theX-ray is so deep that it is difficult to decide the crystallographicorientation in the outermost surface of a specimen. Japanese PatentLaid-open Publication No. H05-264477 (JP, 5-264477A) discloses a methodof analyzing crystallographic orientations of the crystal grains in thesurface layer of a specimen through the use of a X-ray, in which acollimated X-ray is applied to a specimen at a large angle of incidence,i.e., at a grazing angle along the specimen surface and, based on theobtained diffraction circles, the crystallographic orientations of themicrocrystals in the surface layer are measured.

Japanese Patent Laid-open Publication No. 2003-21609 (JP, P2003-21609A)discloses a method of detecting a crystal axis of a specimen using theRutherford backscattering analyzer of the parallel magnetic field typethat has performance of converging the ions back-scattered from thespecimen, the surface of which is irradiated with an ion beam, on thebeam axis through the use of the magnetic field parallel to the incidention beam. In this method, the distribution of detected quantity of thescattered ions is obtained making use of the two-dimensional iondetector and the detection of the crystal axis of the specimen isperformed on the basis of the obtained distribution. This method,however, is problematic in that the measuring devices to be employedtend to be complicated, such as a two-dimensional ion detector, aparallel magnetic field generator and the like and in addition, a longmeasurement time tends to be required for measuring the two-dimensionaldistribution of the scattered ions.

As described above, the EBSP method is widely employed at present as amethod of analyzing and identifying the crystal systems andcrystallographic orientations of the crystal grains on a specimensurface made up of fine crystal grains. The EBSP method, however, isproblematic in that because the electron beam impinges on a specimensurface at a large angle of incidence, minute unevennesses of thesurface affect on the result of the analysis, and that the resolution isof the order of tens of nanometers. While alternatively to the EBSPmethod, there exist methods of analyzing and identifying the crystalsystems and crystallographic orientations of fine crystal grains on aspecimen surface, such methods are not necessarily practical as comparedto the EBSP method.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of crystalanalysis capable of measuring the crystallographic orientations andcrystal systems of crystal grains on a specimen surface with highresolution and with ease.

It is another object of the present invention to provide an apparatusfor crystal analysis capable of measuring the crystallographicorientations and crystal systems of crystal grains on a specimen surfacewith high resolution and with ease.

The density in an image of a scanning ion microscope represents theamount of the secondary electrons emitted from the surface of a specimenin direct correspondence. The amount of the emitted secondary electrons,however, is significantly decreased in the area where the channeling ofthe incident ion takes place, because the incident ion can enter thespecimen to advance into a deep penetration depth in the area. Thus, itis determined that a dark image portion in an image of the scanning ionmicroscope represents the area where the ion channeling takes place.While it has been known so for that the image of the scanning ionmicroscope depends on the ion channeling phenomenon in a specimen, thecase has not been known in which images of a scanning ion microscope areacquired at a variety of angles of incidence of an ion beam with respectto a specimen and the variation in the densities of the acquired imagesis focused on as an object for study.

The present inventors have attained novel knowledge and achieved thepresent invention, wherein the knowledge is that it is possible todiscriminate the crystallographic orientations of the crystal grains ona specimen surface by tracking the variation of density in the image ofthe scanning ion microscope versus a variation of the incidence angle ofthe ion beam. The channeling is a phenomenon closely related to atomicalignments in a crystal, and consequently it is feasible to analyzeatomic arrangements in a crystal based on the variation of the amount ofthe secondary electrons depending on an incidence angle of the ion beam,thereby enabling identification of the crystallographic orientations ofthe crystal grains on the surface of a specimen. In the case where thespecimen has different crystal phases in a mixed phase configuration,the crystal phases and the crystal systems to which respective crystalphases belong, of the crystal grains can be identified as well.

The method of crystal analysis according to the present invention is amethod of analyzing a crystalline state on a surface of a specimen,comprising the steps of; irradiating the specimen with an ion beam;measuring the secondary electrons generated by irradiation of said ionbeam; repeating said irradiating step and said measuring step with eachvariation in an angle of incidence of the ion beam with respect to thespecimen, and determining the crystalline state based on the variationin the amount of the secondary electrons corresponding to the variationof the angle of incidence.

In the present invention, the crystalline state is typically acrystallographic orientation of each of crystal grains present on thesurface of the specimen. In addition, the determination of thecrystalline state can include identification of the crystal phase andthe crystal system to which each crystal grain belongs. Thecrystallographic orientation is determined, for example, based on thedifference between the angle of incidence of the ion beam correspondingto the maximum measured amount of the secondary electrons and the angleof incidence of the ion beam corresponding to the minimum measuredamount of the secondary electrons. The method of crystal analysisaccording to the present invention allows analyzing the crystallographicorientations at a point or in a zone on the surface of a specimen at thesame time in easy combination with the scanning ion microscopicobservations. In this case, the method comprises the steps of:irradiating the specimen while scanning with a focused ion beam;measuring secondary electrons created by the ion beam irradiation toacquire a scanning ion microscopic image: repeating the irradiating stepand the measuring step with each variation in an angle of incidence ofthe ion beam with respect to the specimen, and determining thecrystallographic orientation based on the variation in the densities ofa plurality of the scanning ion microscopic images acquired at differentangles of incidence.

The crystallographic orientation of a crystal can be decided bycalculating a difference between the angle of incidence corresponding tothe darkest image of a plurality of the images of the scanning ionmicroscope and the angle of incidence corresponding to the whitest imagefor each point or zone on the surface of the specimen, and identifyingthe crystallographic orientation based on the calculated difference. Thedifference between an angle of incidence corresponding to the darkestimage and an angle of incidence corresponding to the whitest image isherein referred to as a black-white inversion angle. A variety ofmethods of determining a crystallographic orientation or the like can beenvisaged alternatively to the method based on the black-white inversionangle, as can be known from the study on the channeling of ions in acrystal. It is preferred to decide the crystallographic orientations fora plurality of points or zones on the surface of a specimen andrepresent a distribution of the crystallographic orientations on thesurface of the specimen.

The apparatus for crystal analysis according to the present invention isan apparatus for analyzing a crystallographic orientation at each pointor in each zone on a surface of a specimen, comprising: an ion opticalsystem that irradiates the surface of the specimen scanning with afocused ion beam; a detector that detects secondary electrons generatedby irradiation of the ion beam and provides a detection signal; an imageprocessor that acquires a scanning ion microscopic image based on thedetection signal: an angle adjustment unit that varies an angle of thespecimen with respect to the focused ion beam; a storage device thatstores the scanning ion microscopic images acquired by the imageprocessor; a controller that controls the angle adjustment unit to keepthe angle of the specimen fixed while acquiring each scanning ionmicroscopic image and vary the angle of the specimen with eachacquisition of the scanning ion microscopic image; and acrystallographic orientation calculation unit that determines thecrystallographic orientation based on a variation in densities of aplurality of the scanning ion microscopic images stored in the storagedevice.

The present invention observes the amount of the secondary electronswhen irradiating the surface of a specimen with an ion beam, follows upthe variation in the amount of the second electrons when the angle ofincidence of the ion beam with respect to the specimen varies, andidentifies the crystallographic orientation and crystal system on thespecimen. While the equivalent measurement results can be obtained bymeans of the EBSP method as well which irradiates with an electron beam,the ion beam irradiation at a small angle of incidence, i.e., in theangular direction nearer the normal line of the surface of the specimenaccording to the present invention allows easy comparison of theobserved microscopic images with the identified results of thecrystallographic orientations. Furthermore, in the EBSP method, it isbasically difficult to enhance the resolution, because a diffractionbeam created by means of the Bragg diffraction is employed. In contrast,because the present invention is based on the channeling phenomenon ofions, which are particles, an improvement of the resolution is easy, andit is enabled to determine the crystallographic orientations of finercrystal grains. While the resolution achieved by the EBSP method is theorder of several tens of nanometers, it is enabled according to thepresent invention easily to obtain the resolution of several nanometersand if the diameter of the focused ion beam is made thinner, furtherenhancement of the resolution can be attained.

The method according to the present invention has high affinity to ascanning ion microscopic observation, in which microscopic images areproduced through secondary electrons by ion-beam-scanning the surface ofa specimen, and allows implementing through the use of an existingscanning ion microscope without adding a particular mechanism, providedthat only a mechanism for adjusting the orientation of a specimen isprovided.

The above and other objects, features, and advantages of the presentinvention will become apparent from the following description withreference to the accompanying drawings, which illustrate examples of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the construction of the apparatusfor crystal analysis according to an embodiment of the presentinvention;

FIG. 2 is a scanning ion microscopic (SIM) photograph of a specimen;

FIG. 3 is an inversion pole figure illustrating the processed result bythe EBSP method for the crystallographic orientation of each of thecrystal grains on the surface of the specimen shown in FIG. 2: and

FIG. 4 is a diagram representing the correspondence of the inclinationangles of the specimen in respective zones A to F shown in FIG. 2 toscanning ion microscopic images.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The method of crystal analysis according to the present invention isintended for analyzing the crystallographic orientations and crystalsystems of a specimen surface based on the relation between theintensity of the secondary electron emitted from the specimen when thespecimen surface is irradiated with an ion beam and the angle ofincidence of the ion beam impinging on the specimen. It is possible toobtain the data that represent a two-dimensional distribution of thecrystallographic orientations of crystal grains on a specimen surface byperforming an observation by means of the scanning ion microscope whilevarying the incidence angle of the ion beam with respect to a specimensurface and analyzing a plurality of the scanning ion microscope images(hereinafter referred to as the SIM images) acquired at differentincidence angles. This data representative of the two-dimensionaldistribution is equivalent to an inversion pole figure obtained by themeasurements according to the EBSP method. Thus, the apparatus forcrystal analysis according to an embodiment of the present invention,shown in FIG. 1, represents a scanning ion microscope operated by afocused ion beam, attached with apparatuses required for identifying andanalyzing the crystallographic orientations. Explanation is presentedbelow regarding the apparatus for crystal analysis shown in FIG. 1.

The crystal analysis apparatus is provided with: ion optical system 10and specimen chamber 20 that make up a scanning ion microscope;controller 31 that controls the entirety of the crystal analysisapparatus; image-processor 32 for acquiring SIM images; storage device33 that stores SIM images for respective incidence angles;crystallographic orientation calculation unit 34 that calculates atwo-dimensional distribution of the crystallographic orientations of thespecimen surface based on a plurality of SIM images for differentincidence angles; and output device 35 that displays or prints the SIMimages and the calculated two-dimensional distribution.

Ion optical system 10 is provided with ion source 11 that generates anion beam to be irradiated, condensing optical system 12 that acceleratesand condenses the ion beam carried from ion source 11, and deflectingoptical system 13 that scans the surface of specimen 22 with the focusedion beam in the in-plane directions (X, Y directions) of the surface ofspecimen 13 to perform observations by the scanning ion microscopeGallium ions (Ga⁺) are typically used for the ion beam. Ion source 11,condensing optical system 12 and deflecting optical system 13 arecontrolled by controller 31.

In specimen chamber 20 provided in communication with ion optical system10, there are provided vacuum pump 21 for evacuating ion optical system10 and specimen chamber 20, stage 23 for mounting specimen 22, anddetector 24 for detecting secondary electrons (e⁻) emitted from specimen22 when specimen is irradiated with the ion beam. Stage 23 has atranslation mechanism to displace specimen 22 in X, Y directions andalso is structured to allow inclining specimen 22 to vary the angle ofincidence of the ion beam with respect to specimen 22. In the presentinvention, if it is intended to perform a stricter analysis, then it ispreferred to vary the azimuth of incidence of the ion beam on specimen22 as well. In order to allow not only inclining specimen 22 but alsovarying the azimuth of incidence, as described above, stage 23 is alsoprovided with at least a uniaxial angle adjustment mechanism, preferablymultiaxial angle adjustment mechanism. Stage driver 25 is provided nearspecimen chamber 20 to drive the translation mechanism and angleadjustment mechanism. Stage driver 25 is controlled by controller 31.

Image processor 32 is intended for acquiring the SIM image based on boththe detection signal of the secondary electrons supplied from detectordevice 24 and the synchronization signal synchronized with thedeflection of the focused ion beam in deflecting optical system 13supplied from controller 31. Crystallographic orientation calculationunit 34 calculates a crystallographic orientation for each position orzone on the surface of a specimen on the basis of the variation in thedensity of the SIM image when the angle of incidence of the ion beam isvaried at each position or zone. It is possible in the presentembodiment to calculate crystal systems of crystal grains at respectivepositions or zones as well if different crystal phases are mixedlypresent in the specimen.

Explanation is next given regarding a crystal analysis through the useof the above-described crystal analysis apparatus.

Specimen 22 is first mounted on stage 23, the ion beam supplied from ionsource 11 is focused by condensing optical system 12, the focused ionbeam is deflected by deflecting optical system 13 to irradiate thesurface of specimen 22 so as to scan two-dimensionally. The secondaryelectrons emitted from specimen 22 are detected by detector 24, whichgenerates a detection signal corresponding to the amount of thesecondary electrons. Image processor 32 acquires the SIM image based ofthis detection signal and the synchronization signal supplied fromcontroller 31, supplies the SIM image to output device 35 and alsostores the SIM image in storage device 33. Controller 31 controls stagedriver 25 to keep the angle of incidence of the ion beam with respect tospecimen 22 fixed while acquiring one SIM image, and to vary the angleof incidence of the ion beam with respect to specimen 22 bit by bit witheach acquisition of the SIM image. This control operation on stagedriver 25 allows image processor 32 to successively acquire SIM imagesfor differing angles of incidence of the ion beam and all of theacquired SIM images are stored in storage device 33.

When a sequence of the SIM images has been acquired for a predeterminedrange of the angle of incidence and stored in storage device 33,crystallographic orientation calculation unit 34 next reads out the SIMimages from storage device 33, calculates the distribution of thecrystallographic orientations within an observation zone in the surfaceof specimen 22 on the basis of the variation in density of the SIM imagedepending on the variation of the angle of incidence of the ion beam,and delivers the calculated results to output device 35 as, for example,a distribution diagram. As a result, a result of analysis can beobtained similar to the inversion pole figure by means of the EBSPmethod.

Explanation below regards the results obtained through actualmeasurements according to the method of crystal analysis of the presentinvention.

In the measurements, copper formed by the plating process was employedas a specimen. A copper crystal belongs to the cubic system and has theface-centered cubic lattice structure. With each change in the angle ofincidence of the ion beam with respect to the specimen, an SIM image ofthe specimen was acquired by the scanning ion microscope using thefocused ion beam. Gallium ions were employed for the ion beam, and 30 kVof the acceleration voltage and 10 pA of the specimen current wereapplied.

FIG. 2 represents an SIM image of a specimen when irradiating thespecimen with an ion beam at an inclination angle of 0 degrees of thespecimen, i.e., along the normal line of the specimen surface. Theobservation zones are set in this specimen as illustrated in A to F.FIG. 3 represents the inversion pole figure created for the samespecimen by the EBSP method. While an inversion pole figure is commonlyrepresented by a color picture, it is herein represented by a monochromegrayscale picture. The measurement conditions in the EBSP method are 20kV of the acceleration voltage and 70 degrees of the inclination angleof the specimen.

FIG. 4 represents the variation of the SIM images at intervals of 5degrees of the inclination angle of the specimen in each of zones A to Fshown in FIG. 2. The crystallographic orientation of each observationzone was identified in advance on the basis of the inversion polefigures shown in FIG. 3. Each of the images in the top row of FIG. 4represents an inversion pole figure for each observation zone.

As known from FIG. 4, varying the inclination angle of the specimenyielded a definite change in the grayscale shade of the SIM image. Afurther analysis proved that there is a correlation between a half valueof an angle of each crystallographic plane making with respect to 001plane and the variation in the inclination angle that causes thecontrast to vary from the maximum value of white to the maximum value ofblack, or from the maximum value of black to the maximum value of white.The angle variation that causes an SIM image to vary from the maximumvalue of white to the maximum value of black, or from the maximum valueof black to the maximum value of white is referred to as a black-whiteinversion angle. Table 1 represents the black-white inversion anglemeasured for each crystal plane. TABLE 1 Zone A B C D E F Crystal plane001 321 101 201 111 101 211 301 Angle (°) of 0 36.7 45 26.6 54.7 45 35.318.4 each plane that makes with 001 plane of cubic system Half value of0 18.4 22.5 13.3 27.4 22.5 17.7 9.2 angle that makes with 001 planeMeasured 5 15 20 15 25 20 10 10 black-white inversion angle

In addition, the ranges of angles corresponding to the measuredblack-white inversion angles are represented by two-headed arrows inFIG. 4. In this regard, only the 001 plane exhibited a differentbehavior, i.e., the grayscale shade of the image suddenly changes at acertain angle from white to black or from black to white, rather thangradually changes.

From the measured results described above, it is proved that theblack-white inversion angle equals a half of an angle a crystal plane ofinterest makes with 001 plane and thus the crystallographic orientationin a desired position or zone in an SIM image can be discriminated bymeasuring the black-white inversion angle in the subject position orzone. Further, it is possible to identify the crystallographicorientation further strictly by taking into account an actual range ofthe inclination angle of the specimen corresponding to the black-whiteinversion angle, taking into account the pattern of the variation in thedensity or grayscale shade of the image, and changing the azimuth ofincidence of the ion beam. Still further, it is also possible todetermine the crystallographic orientation without measuring ablack-white inversion angle by settling a plurality of angles ofincidence used for the measurements in advance and simply comparing thedensities or grayscale shades of the SIM images acquired at therespective settled angles.

As described above, the method of crystal analysis and the apparatus forcrystal analysis according to the present invention allow the analysisand identification of the crystallographic orientations and crystalsystems of fine crystal grains on the surface, thereby serving for theanalysis of defectives and improvement in manufacturing management by,for example, applying to the measurements of the crystallographicorientations of a conductive layer and a semiconductor layer in themanufacture of a semiconductor device. Furthermore, the presentinvention offers advantages of improving the quality of products,obviating production of defectives and improving manufacturingprocesses, in the fields where the crystalline state and thecrystallographic orientation of the material to be used affect thequality of the product.

While preferred embodiments of the present invention have been describedusing specific terms, such description is for illustrative purposesonly, and it is to be understood that changes and variations may be madewithout departing from the spirit or scope of the following claims.

1. A method of analyzing a crystalline state on a surface of a specimen,comprising the steps of: irradiating said specimen with an ion beam;measuring the secondary electrons generated by irradiation of said ionbeam; repeating said irradiating step and said measuring step with eachvariation in an angle of incidence of said ion beam with respect to saidspecimen, and determining said crystalline state based on the variationin amount of said secondary electrons corresponding to the variation ofsaid angle of incidence.
 2. The method according to claim 1, whereinsaid crystalline state is a crystallographic orientation of each ofcrystal grains, and said crystallographic orientation is determinedbased on a difference between the angle of incidence of said ion beamcorresponding to maximum measured amount of said secondary electrons andthe angle of incidence of said ion beam corresponding to minimummeasured amount of said secondary electrons.
 3. A method of analyzing acrystallographic orientation at a point or in a zone on a surface of aspecimen, comprising the steps of: irradiating said specimen whilescanning with a focused ion beam; measuring secondary electronsgenerated by irradiation of said ion beam to acquire a scanning ionmicroscopic image, repeating said irradiating step and said measuringstep with each variation in an angle of incidence of said ion beam withrespect to said specimen, and determining said crystallographicorientation based on the variation in densities of a plurality of saidscanning ion microscopic images acquired at different angles ofincidence.
 4. The method according to claim 3, wherein for said point orzone on the surface, a difference between the angle of incidencecorresponding to a darkest image of a plurality of said scanning ionmicroscopic images and the angle of incidence corresponding to a whitestimage is calculated, and said crystallographic orientation at a point orin a zone is decided on a basis of said difference.
 5. An apparatus foranalyzing a crystallographic orientation at each point or in each zoneon a surface of a specimen, comprising: an ion optical system thatirradiates the surface of the specimen scanning with a focused ion beam;a detector that detects secondary electrons generated by irradiation ofsaid ion beam and provides a detection signal; an image processor thatacquires scanning ion microscopic images based on said detection signal;an angle adjustment unit that varies an angle of said specimen withrespect to said focused ion beam; a storage device that stores thescanning ion microscopic images acquired by said image processor; acontroller that controls said angle adjustment unit to keep said angleof said specimen fixed while acquiring one scanning ion microscopicimage and varies said angle of said specimen with each acquisition ofsaid scanning ion microscopic image; and a crystallographic orientationcalculation unit that determines said crystallographic orientation basedon a variation in densities of a plurality of said scanning ionmicroscopic images stored in said storage device.
 6. The apparatusaccording to claim 5, wherein said crystallographic orientationcalculation unit calculates, for said point or zone on the surface, adifference between the angle of incidence corresponding to a darkestimage of a plurality of said scanning ion microscopic images and theangle of incidence corresponding to a whitest image, and decides saidcrystallographic orientation at a point or in a zone on a basis of saiddifference.
 7. The apparatus according to claim 6, wherein saidcrystallographic orientation calculation unit provides an output of dataindicating a distribution of said crystallographic orientations on thesurface of said specimen.